Work out your most fertile days

We’ll show you how to figure out when you’re most likely to get pregnant.

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Timing is everything when you’re trying to get pregnant. Understanding your ovulation cycle and learning to read your body’s signs can help you predict your most fertile days and increase your chances of falling pregnant quickly.

Why ovulation is important

When you ovulate, an egg is released from your ovary and ready to be fertilised. Eggs live between 12–24 hours after ovulation, while sperm can live up to 5 days inside you, so the 5 days before and the 2 days after ovulation are your most fertile days. If you have a fairly accurate idea of when you’re going to ovulate, you can boost your chances of getting pregnant.

Start with a chart

Keeping track of your cycle is the first step to working out your fertile days. Mark the first day of your period on your calendar as day 1 of your cycle. Continue to mark each day until the first day of your next period, which you should mark as day 1 again. Chart your cycle for at least 3–4 months. The more cycles you chart, the more reliable your calculations will be.

Count the number of days in your cycles. Then subtract 18 from the number of days in your shortest cycle e.g. if your shortest cycle is 26, then subtract 18 from 26, which gives you 8. Subtract 11 from the number of days in your longest cycle e.g. if your longest cycle is 31, then subtract 11 from 31 which gives you 20. Mark days 9–20 of your cycle as your most fertile days.

Day your fertile period starts = No. of days in your shortest cycle – 18

Day your fertile period ends = No. of days in your longest cycle – 11

Make your prediction more accurate

The calendar method we used to calculate your fertile days gives you a much larger window than we know is possible. You can make your chart more accurate by paying attention to your basal body temperature and the changes in your cervical mucus to help narrow your window.

Your cervical mucus is usually dry just after your period and after ovulation. As you get closer to ovulation, cervical mucus increases. It might be yellowish or cloudy and sticky at first and slowly becomes runnier and clearer, until it starts to resemble egg white. The day when you have the largest amount of clear, stretchy, slippery cervical fluid is the day you’re most fertile, usually the day before or the day of ovulation. Add this day to your chart for a few months until you begin to see a pattern.

Usually your basal body temperature spikes 2 or 3 days after ovulation. So take your temperature every day and add it to your chart. Mark the days your temperature spikes for a few months.

By charting your cervical mucus and basal temperature for a few months, you should be able to identify your most likely ovulation day and narrow the window of your fertile days.

If you experience other symptoms such as tender breasts or a pain in your side when you ovulate, you can chart those symptoms too.

Get the timing right

You’ll want to have sex a day or 2 before you ovulate and again on the day you ovulate. It takes time for sperm to swim up to the egg, so with this approach, you ensure that there is a healthy amount of sperm waiting in the fallopian tube when the egg is released.

Having sex only during your fertile period is efficient since you can only get pregnant on your fertile days. However, predicting when you ovulate is an informed guess at best and the only fool proof way to get pregnant is to have sex regularly every 2 days throughout your cycle.